Recently, we obtained several cDNA clones encoding the RS viral nucleocapsid protein (NC), matrix protein (M), phosphoprotein (P) and a nonstructural protein (NS2) (Venkatesan et al., PNAS, 1983). We have since sequenced a cDNA plasmid encoding the entire coding sequence of the NC gene. The 3 foot terminus of this gene has been identified by the presence of 14 poly A residues at one end of the clone. The cloned DNA lacks 6 nucleotides of the 5 foot end of the mRNA as determined by primer extension and gene walking on the mRNA. However, a single open reading frame of 1412 nucleotides encoding a protein of 467 amino acids is present within the cloned DNA. This translated protein of 51540 daltons is rich in basic amino acids, relatively rich in proline, but poor in cysteine. It has no sequence homology with the capsid proteins of other negative strand RNA viruses implying that RS virus is evolutionarily distinct. Interestingly, the sequence upstream of the poly A tail of this gene was not homologous to a similar region in the other RS viral genes.